1. Field of the Invention
The parent application relates to methods for treating a work piece with a One Atmosphere Uniform Glow Discharge Plasma (OAUGDP), and the work piece so obtained.
2. Description of the Related Art
The OAUGDP is a very useful technology to modify substrates to impart to the substrates desirable properties. Basic information on plasma physics and the physical processes important in industrial plasma is found in Industrial Plasma Engineering, Vol. 1, J. Reece Roth, 1995, (Institute of Physics Publishing, Bristol and Philadelphia, Pa.). Low power plasmas known as dark discharge coronas have been widely used in the surface treatment of thermally sensitive materials such as paper, wool and synthetic polymers such as polyethylene, polypropylene, polyolefin, nylon and poly(ethylene terephthalate). Because of their relatively low energy content, corona discharge plasmas can alter the properties of a material surface without damaging the surface.
Glow discharge plasmas represent another type of plasma, the relatively low power densities of which are useful for non-destructive material surface modification. However, glow discharge plasmas have heretofore been successfully generated typically in low pressure or partial vacuum environments below 10 Torr. Such plasma deposition, as by chemical vapor deposition under vacuum requires batch processing, expensive vacuum equipment and is of limited versatility.
Low pressure or vacuum electrical discharges should be distinguished from low power density filamentary plasmas at one atmosphere which have been used for ozone production. Such plasmas are not satisfactory for the treatment of substrates, in particular because unlike the OAUGDP, they do not treat the substrates evenly and tend to damage the surface of the substrate. OAUGDP, in contrast, has none of these disadvantages and has important technical and economic advantages of particular interest for the present invention.
The present invention deals with the treatment of a substrate with OAUGD to render the substrate impervious to oxygen with a coating of silicon oxides. Particularly, the invention deals with substrates like plastics and paper laminates designed for food containers.
For background patents of interest, the following patents may be consulted: U.S. Pat. No. 5,403,453, Method and Apparatus For Glow Discharge Plasma Treatment of Polymer Materials at Atmospheric Pressure, Roth et al., 1995; U.S. Pat. No. 5,414,324, One Atmosphere, Uniform Glow Discharge Plasma, Roth et al., 1995; U.S. Pat. No. 5,387,842, Steady-State, Glow Discharge Plasma, Roth et al., 1995; U.S. Pat. No. 5,456,972, Method and Apparatus For Glow Discharge Plasma Treatment of Polymer Materials at Atmospheric Pressure, Roth et al., 1995; U.S. Pat. No. 5,508,075, Packaging Laminate With Gas and Aroma Barrier Properties, Roulin et al., 1996; U.S. Pat. No. 5,133,999, Packaging Material of Laminate Type, Lofgren et al. 1992; U.S. Pat. No. 4,495,016, Method of Making a Packing Laminate Web, Viberg et al., 1985; U.S. Pat. No. 5,224,441, Apparatus for Rapid Plasma Treatments and Method, Felts et al. 1993; and, U.S. Pat. No. 5,506,036, Easy-to-Recycle Laminated Material For Packaging Use, Bergerioux, 1996, all of which are incorporated herein by reference.
In prior art processes utilizing PECVD, the plasma is formed in an enclosed reaction chamber in which the substrate is positioned and from which the air is evacuated until a high vacuum is achieved. A substrate thin film may be repeatedly moved back and forth within the plasma reaction chamber in order to deposit multiple layers on the substrate. When this is accomplished, the substrate is removed from the deposition chamber, and another batch of substrate is introduced into the chamber and the operation is repeated, thus typically operating the PECVD by batch processing. Another shortcoming of the PECVD is that the substrate must be a vacuum compatible material. See, U.S. Pat. No. 5,888,199, Plasma Thin Film Deposition Process, Felts et al, 1989.
U.S. Pat. No. 5,508,075 to Roulin et al. relates to a laminate having a substrate on which a layer of silicon oxides is applied by chemical plasma vapor deposition under vacuum. The plasma enhanced chemical vapor deposition (PECVD) method to deposit SiO.sub.x on packaging substrates is a development in response to the practice common in the United States, Europe and elsewhere in the world to provide packaging laminates, for instance for the manufacture of cartons for liquid, like milk or fruit juice, with a layer of aluminum foil to minimize the penetration of oxygen into the carton and the degradation of the flavor oils or the loss of flavor or color from the package. However, aluminum will not be acceptable any longer in areas when and where environmental regulations prohibit its use and disposal.
The present invention is an improvement over the known technique of PECVD of silicon oxides on a substrate.